The present invention relates to a fuel pump, and particularly to a slipper pump for pumping low viscosity fuels such as gasoline or the like to an internal combustion engine of an automotive vehicle.
Certain fuel pumps are subject to rather significant noise problems. Noise is a particular problem with fuel pumps which supply fuel to a fuel injector system. Such fuel pumps are normally mounted in association with the fuel tank of the vehicle. Thus, noise produced by the pump reacts with the sheet metal of the tank, and an unacceptable noise level results.
Also, fuel pumps which are mounted in association with the fuel tank of a vehicle are subject to cavitation. Low viscosity fuels have a tendency to vaporize, and thus bubbles form in the fuel being pumped. These bubbles affect the fuel flow rate from the pump and the vacuum level at the pump inlet. A typical solution for attempting to avoid cavitation is to attempt to completely fill the pumping pockets of the pump. This is done by providing suitable inlet porting for the pumping pockets.
In the case of slipper pumps, fuel has been directed into the expanding pockets of a slipper pump through a pair of inlet ports. These ports are located so that one port provides a major portion of the flow into the pumping pockets and a second port provides for a flow of fluid into the pumping pockets at a location under the slipper. U.S. Pat. No. 4,080,124, for example, discloses such a pump. Such a pump does provide for maximum flow into the pumping pockets. However, such port configurations also results in substantial noise and/or less than optimum inlet suction capability. The noise is believed to be created (1) due to the flow eddies within the pump between the two inlet ports and (2) due to the bursting of vapor bubbles, which may have become located in a pumping pocket, during operation of the pump.
The present invention is directed to a slipper pump for pumping low viscosity fuel and adapted to be mounted in association with the fuel tank of a vehicle. In particular, the present invention is directed to a slipper pump which has low cavitation, relatively high output flow rate and inlet vacuum, and in which the aforementioned noise is restricted. Thus, the pump of the present invention may be mounted in association with a fuel tank without creating the noise made by other pumps.
More specifically, the present invention is directed to a fuel pump of the slipper type in which, in addition to an inlet port configuration, an orifice of a predetermined size is located to communicate fuel inlet with the area beneath the slipper in the inlet arc of the pump. Specifically, it has been found that by providing an orifice which communicates the fuel inlet with the area beneath the slipper, the noises produced in the pump are restricted. Further, it has been found that through the use of such an orifice a relatively high vacuum can be maintained at the pump inlet and high flow rates can be achieved from the pump.
The particular size of the orifice is important, and the particular size may vary from pump to pump depending upon the fuel which is being pumped and the rate of volume change in the pumping pockets in the pump inlet and outlet. The concept is that by throttling the flow of fluid into the pumping pockets beneath the slipper significantly improved pump performance can be achieved, particularly if the throttling orifice is properly sized.
Orifices having a diameter falling within the range of 0.067 inches to 0.076 inches have been found to be satisfactory for slipper pumps tested. Further, it has been found through testing that an orifice diameter in general accordance with the following equation provides a slipper pump with relatively high inlet vacuum, a low noise level, and relatively high fuel flow rate. The equation is: EQU Y=-0.15066X.sup.2 +5.1196X+33.165
where:
Y=orifice diameter in thousandths of an inch and
X=cam stroke in thousandths of an inch.
As is known, cam stroke, also referred to as cam rise, determines the amount of radial movement of a slipper during pump operation. It affects the rate of change in volume of the pumping pockets of a slipper pump.
The aforementioned formula has been derived by a computer which has been supplied test data. The formula thus is an approximation of the best orifice diameter for a pump having a given cam stroke.